Studies on animal lentiviruses have led to the development of potential vaccines for equine infectious anemia. Equine infectious anemia virus (EIAV) Pr55gag expressed in bacterial and vaccinia virus systems are undergoing tests for efficacy. The transcriptional patterns of EIAV and caprine arthritis encephalitis virus (CAEV) have been studied and reveal mRNAs specific for potential viral regulatory genes. The isolation of an infectious molecular clone of EIAV will facilitate understanding of determinants of lentivirus pathogenicity. A number of molecular clones of defective forms of the CAEV genome were isolated from unintegrated DNA and their effects on the course of CAEV infections are being determined. The nucleotide sequences of the human dbl oncogene and proto- oncogene have been determined and analyzed. The results show that dbl represents a new class of transforming gene and that the proto- dbl translational product shares features with proteins that constitute structural elements of cells. The chromosomal localization of dbl oncogene sequences has been determined. These studies show that dbl was generated by recombination between three sequences originating from two different human chromosomes.